In certain process technologies, involving two-phase flows, a need exists for preferentially letting out liquid from a confined space.
One typical example can be found in hydroprocessing reactors operating with low boiling point feeds. At regular operating conditions, such reactors treat a gas-phase feed. However, during start-up, when the system is cold the feed is fully or partially in the liquid phase, any confined space where the liquid may accumulate inside such reactors may be subject to the risk of malfunctioning.
This situation can occur on scale catching trays installed inside naphtha hydrotreaters.
Such trays are installed in units experiencing pressure drop problems when particles of different origins as well as products of corrosion, brought to the reactor from upstream equipment, accumulate on the grading or catalyst beds. In order to extend the unit cycle length and to manage pressure drop development over time, in some reactors of those units various types of particle/scale catcher systems are installed. Even though, the gas phase is the only phase in the reactors during normal operations, these particle/scale catching systems must be able to handle liquid too.
The liquid is delivered to the reactor(s) at startup, during the period from feed introduction to the moment when the reactor inlet temperature is higher than the final boiling point of the startup feed. As the period is in the range of a few hours, a lot of the liquid is delivered and any installed tray in the reactor must be designed to enable transfer of the liquid to the next level.
In the art, this problem is commonly solved by installation of liquid transfer tubes. One of the drawbacks of these systems is that, those tubes stay open during all cycle length and the process gas containing particles and scales can bypass the scale catching system.
There is therefore a need for a valve technology that opens when liquid is in the tray, preferentially allowing the flow of liquid downstream, but closes if liquid is absent, so that the gas is treated and the scale catching trays can perform its function on all of the feed in gas-phase, without any by-pass.
U.S. Pat. No. 5,989,414 discloses a self-adjusting extraction nozzle for extracting a surface disposed over a base fluid including a suction tube having at least one slot extending there through. A nozzle channel extends outwardly from the at least one slot. The nozzle channel is slidably coupled to the exterior of the suction tube and to a float to support the nozzle channel at a level of the surface fluid.
U.S. Pat. No. 5,009,079 describes a simple flow control device in a condensate drain pipe to prevent the flow of refrigerant vapour there through and to regulate the flow of liquid refrigerant as a function of the level of accumulated liquid refrigerant in the drain pipe. The only moving part is a float device that rides up on a cylindrical valve body in response to the level of liquid refrigerant to thereby expose slots in the valve body which allow for the flow of liquid refrigerant to the refrigerant return line to the cooler.
US2009158763 discloses a refrigerant floating expansion apparatus including a main body, a standpipe, a float element and a separation element. The main body includes a base plate and a pipe-shaped housing. The standpipe fixed on the base plate has a second pipe opening and a third pipe opening. The pipe wall of the standpipe has at least an opening near the second pipe opening. The float element surrounds the standpipe for controlling a fluid-passing area of the opening. The separation element surrounding the float element is disposed on the base plate and forms an inner path with the pipe-shaped housing. The separation element has several fluid passageways near the base plate. A high-pressure fluid entering the main body is guided to pass through the fluid passageways to move the float element for controlling the fluid-passing area of the opening. Then, the high-pressure fluid is transferred to a low-pressure fluid.
In spite of the above mentioned known art, a need exists for a robust valve which can operate in harsh environments with elevated temperature and pressure and in surroundings with impurities.